Is this pilot the provision I prayed to God for, and is my rejection of him considered a sin after my prayer for marriage?

Supplication (Du'a) is one of the best means to achieve one's desired outcome. However, it cannot be asserted that the man who proposed is the one for whom the supplication was made, as this is part of the unseen, known only to Allah. There is no obligation to accept marriage to him. Rejecting a competent suitor is neither a sin nor a rejection of sustenance from Allah. If trustworthy individuals praise him well, then one should seek Allah's guidance (Istikhara) regarding marriage to him, and what results from Istikhara will be good.